This project is a continuation of my X-ray crystallographic investigations of the molecular structures of membrane phospholipids. The aim of these studies is to understand how these lipids contribute to the structure and function of biological membranes. New data has been collected on dimyristoyl phosphatidylcholine dihydrate extending nearly to the limits of the Cu Ewald Sphere. The preliminary report of this structure has already been published (R equals 17% in Nature, Vol. 281 (1979), p. 499). The new data will enable further refinement of the structure. This should give precise bond distances for the water structure and provide more detail on the hydrocarbon chain packing in this crystal. The highly purified crystalline lecithin will be used for growing other forms of this compound (i.e. other hydration states). In addition, other lecithins and other phospholipids will be investigated crystallographically.